For various applications with demanding synchronisation constraints, for example the synchronisation of base stations of a mobile network, methods for the distribution of a reference time and/or a reference frequency on the packet-switching networks are being developed. For example, a Network Time Protocol (NTP) work group of the IETF is developing an upgrade to the NTP protocol initially specified in RFC 1305. The Precision Time Protocol (PTP) of the IEEE has recently been revised with this in mind. The ITU-T has defined a physical layer technology for the distribution of a reference frequency on an Ethernet network, called Synchronous Ethernet and described in the specifications G.8261, G.8262 and G.8264.
The document “IEEE-1588 and Synchronous Ethernet in Telecom”, in “2007 International IEEE Symposium on Precision clock Synchronization for Measurement, Control and Communication” pp 138-142 describes a network with a core network in which the synchronisation is distributed by Synchronous Ethernet to a network edge and an access network in which the IEEE-1588 Version 2 protocol is used to prolong the synchronisation chain from the network edge to access devices. At the edge, a type 1588 master clock retrieves the frequency distributed by the Synchronous Ethernet core network.